The present invention relates to a resin composition, a molded product employing it and an electroconductive sheet. Said electroconductive sheet is useful for packaging containers for semiconductors such as IC and electronic parts, particularly useful for carrier tapes.
For packaging IC, electronic parts using IC or electronic parts, injection-molded trays, vacuum-formed trays, magazines, carrier tapes (referred to also as embossed carrier tapes) etc. have been used. To prevent breakage of electronic parts such as IC due to static electricity, as the packaging containers, ones having an electroconductive filler dispersed therein have been used. As the electroconductive filler, carbon black is widely used, with which a stable surface resistivity will be obtained constantly at a low cost.
An electroconductive sheet comprising a thermoplastic resin having carbon black dispersed therein, has such drawbacks that (1) mechanical strength and processability will decrease, and (2) an electronic part will be stained by falling off of the resin containing carbon black on the surface of the electroconductive sheet by abrasion of the packaged electronic part with the electroconductive sheet. JP-A-57-205145, JP-A-62-18261, etc. have been proposed as a method to overcome the problem (1), and JP-A-9-7624, JP-A-9-76425, etc. have been proposed as a method to overcome the problem (2). However, electronic parts are getting more complex, precise and small, and packaging and mounting of electronic parts proceed at a higher speed at the present time, and accordingly, an electroconductive sheet for packaging an electronic part, which is less likely to cause staining of the electronic part, and which has improved mechanical strength, has been desired.
The present invention provides an electroconductive sheet for packaging an electronic part, which substantially reduces staining of the electronic part due to abrasion of the electroconductive sheet with the electronic part, and which has adequate mechanical strength to endure packaging or mounting at a high speed, and a packaging container for an electronic part. The electroconductive sheet is particularly useful for a carrier tape.
The present invention provides an electroconductive sheet comprising a substrate layer and having laminated on at least one side of the substrate layer, a surface layer of an electroconductive resin composition comprising a polycarbonate type resin and from 5 to 50 wt % of carbon black based on the polycarbonate type resin. Said electroconductive sheet is useful as an electroconductive sheet for packaging an electronic part, and said electroconductive sheet for packaging an electronic part is useful as a packaging container for an electronic part, particularly as a carrier tape.
As a constitution of the electroconductive sheet, a two-layer structure of surface layer/substrate layer, wherein the surface layer comprises an electroconductive resin composition and is placed on the side which will be in contact with the electronic part, is preferred. Further, a constitution of surface layer/substrate layer/surface layer is also preferred. Another layer may be provided between the surface layer and the substrate layer.
The polycarbonate type resin for the electroconductive resin composition is not particularly limited, and an commercially available product may be used. For example, an aromatic polycarbonate resin, an aliphatic polycarbonate resin and an aromatic-aliphatic polycarbonate may be mentioned. One obtained by polycondensation of a conventional bisphenol A with phosgene or by polycondensation of bisphenol A with carbonic acid ester, which is usually classified into an engineering plastic, may also be used. This is composed mainly of bisphenol, and produced by a phosgene method or by ester exchange, and the bisphenol to be used as the raw material may, for example, be 2,2-bis-(4-hydroxyphenyl)propane (bisphenol A), 2,4-bis-(4-hydroxyphenyl)-methyl-butane or 1,1-bis-(4-hydroxyphenyl)-cyclohexane. A homopolycarbonate, a copolycarbonate obtained by copolymerization of a carboxylic acid, or a mixture thereof, may also be used.
Carbon black to be incorporated in the electroconductive resin composition may, for example, be furnace black, channel black or acetylene black, and preferred is one having a large specific surface area and whereby a high level of electroconductivity can be obtained with a small amount of incorporation to the resin, such as KETJENBLACK or acetylene black.
The amount of carbon black to be incorporated in the electroconductive resin composition is preferably from 5 to 50 wt % based on the polycarbonate type resin. If it is less than 5 wt %, no adequate surface resistivity will be obtained to prevent breakage of an electronic part due to static electricity. If it exceeds 50 wt %, the fluidity will decrease, whereby it may be difficult to laminate the electroconductive resin composition on the substrate layer, and the mechanical strength of the electroconductive sheet to be obtained will also decrease.
The surface resistivity of the electroconductive sheet on the side on which the electroconductive resin composition is laminated, is preferably from 102 to 1010 xcexa9. If it is beyond this range, it tends to be difficult to prevent breakage of an electronic part due to static electricity.
Into the electroconductive resin composition, another resin component such as an acrylonitrile-butadiene-styrene copolymer type resin or a polybutylene terephthalate resin may be incorporated as a modifier.
As the modifier, a graft resin of an ethylene-glycidylmethacrylate type copolymer with an acrylonitrile-styrene type copolymer is suitably used. The electroconductive resin composition in this case comprises a polycarbonate type resin, and from 5 to 50 wt % of carbon black and at most 40 wt % of a graft resin of an ethylene-glycidylmethacrylate type copolymer with an acrylonitrile-styrene type copolymer, based on the polycarbonate type resin. The electroconductive resin composition may be made of a polycarbonate type resin, carbon black and a graft resin alone, or may be composed mainly of those and contain another component within a range of not impairing the purpose of the present invention.
The graft resin of an ethylene-glycidylmethacrylate type copolymer with an acrylonitrile-styrene type copolymer is a resin obtained by grafting an acrylonitrile-styrene type copolymer to an ethylene-glycidylmethacrylate type copolymer, and a resin obtained by grafting an acrylonitrile-styrene type copolymer having an acrylonitrile content of at most 50 wt % to an ethylene-glycidylmethacrylate type copolymer having a glycidylmethacrylate content of at most 45 wt %, is suitably used, which is commercially available.
The amount of the graft resin to be incorporated is at most 40 wt %, preferably from 1 to 40 wt %, more preferably from 3 to 40 wt %, based on the polycarbonate type resin. Within the above range, the mechanical strength, particularly impact strength, will be improved to endure packaging and mounting of electronic parts at a high speed. If it exceeds 40 wt %, the elastic modulus will decrease.
When the above resin composition is used for an electroconductive sheet as an electroconductive resin composition, it may be used as a monolayer electroconductive sheet or a multilayer electroconductive sheet. It may be used as a molded product by itself.
Into the electroconductive resin composition, an additive such as a lubricant, a plasticizer or a processing aid may further be incorporated as the case requires.
The electroconductive sheet is particularly useful as a carrier tape. For such an application, an electroconductive sheet for a carrier tape, which has a reduced reflection on the surface, has been desired so as to prevent malfunction of an inspection machine due to reflection on the surface of the electroconductive sheet at the time of image inspection of e.g. IC. According to the present invention, the layer of an electroconductive resin composition has a surface roughness Ra of from 0.6 xcexcm to 4.0 xcexcm, whereby malfunction of an inspection machine due to reflection on the electroconductive sheet surface can be prevented at the image inspection of electronic parts such as IC. If the surface roughness Ra is less than 0.6 xcexcm, the surface gloss tends to be high, whereby the machine will malfunction due to reflection on the electroconductive sheet surface at the image inspection, and if it exceeds 4.0 xcexcm, the surface of the electroconductive sheet tends to be too rough, and the appearance of the sheet tends to be poor, and the sheet is thereby not suitable as an electroconductive sheet for a carrier tape. Here, the surface roughness Ra is a centerline surface roughness in accordance with JIS-B-0651.
As a substrate layer, preferred is one comprising an acrylonitrile-butadiene-styrene copolymer type resin and/or a polystyrene type resin, one comprising a polyethylene terephthalate type resin and a polycarbonate type resin, or one comprising an imidated copolymer having an aromatic vinyl monomer residue and an unsaturated dicarboxylic acid imide derivative residue. Another component may be incorporated into the substrate layer within a range of not impairing the purpose of the present invention.
An electroconductive sheet comprising a substrate layer of a thermoplastic resin comprising an acrylonitrile-butadiene-styrene copolymer type resin and/or a polystyrene type resin and having laminated on at least one side of the substrate layer, an electroconductive resin composition comprising a polycarbonate type resin and from 5 to 50 wt % of carbon black, is one of preferred constitutions of the electroconductive sheet.
The acrylonitrile-butadiene-styrene copolymer type resin to be used in the present invention is one composed mainly of a copolymer consisting essentially of three components of acrylonitrile, butadiene and styrene, and a commercially available product may be used. For example, a copolymer obtained by block or graft polymerization of at least one monomer selected from an aromatic vinyl monomer and a vinyl cyanide monomer to a diene type rubber, or a blended product with said copolymer, may be mentioned. Said diene type rubber is a polymer obtained by polymerizing butadiene as a component, and examples of which include polybutadiene, polyisoprene, an acrylonitrile-butadiene copolymer and a styrene-butadiene copolymer. The aromatic vinyl monomer may, for example, be styrene, xcex1-methylstyrene or an alkyl-substituted styrene. The vinyl cyanide monomer may, for example, be acrylonitrile, methacrylonitrile or a halogen-substituted acrylonitrile. Specific examples of the copolymer and the blended product with said copolymer include an acrylonitrile-butadiene-styrene terpolymer and one obtained by polymer-alloying a polybutadiene to an acrylonitrile-styrene bipolymer. Further, an acrylonitrile-styrene bipolymer containing no rubber component is also included.
The polystyrene type resin is a polymer obtained by polymerizing styrene as a component, and examples of which include one composed mainly of a polystyrene resin for general use or an impact resistant polystyrene resin, or a mixture thereof.
In a case where the substrate layer for the electroconductive sheet is made of at least one thermoplastic resin selected from the group consisting of an acrylonitrile-butadiene-styrene copolymer type resin and a polystyrene type resin, a polycarbonate type resin may further be incorporated in an amount of from 1 to 50 wt % based on the thermoplastic resin. By incorporating a polycarbonate type resin, the mechanical strength will further be improved. The amount of the polycarbonate type resin is preferably at most 50 wt % so as to obtain an electroconductive sheet at a low cost.
In a case where a polyethylene terephthalate type resin and a polycarbonate type resin are used for the substrate layer, the proportion of the polyethylene terephthalate type resin is preferably from 35 to 97 wt %, and the proportion of the polycarbonate type resin is preferably from 3 to 65 wt %, based on the total amount of the two components. In such a case, another component may be incorporated therein within a range of not impairing the purpose of the present invention.
As the polycarbonate type resin, one used for the electroconductive resin composition for the surface layer may be used. The resin for the substrate layer may be the same as or different from one used for the surface layer. Preferably, the polyethylene terephthalate type resin is from 35 to 97 wt %, and the polycarbonate type resin is from 3 to 65 wt %, and more preferably, the polyethylene terephthalate type resin is from 51 to 97 wt %, and the polycarbonate type resin is from 3 to 49 wt %, based on the total amount of the polyethylene terephthalate type resin and the polycarbonate type resin. The folding strength and the secondary processability of the electroconductive sheet will decrease if the compounding ratio of the polycarbonate type resin is too low or too high. The balance of the strength and the secondary processability will be excellent within the above-mentioned ranges.
The polyethylene terephthalate type resin may be one composed mainly of ethylene glycol and terephthalic acid or a dimethyl ester thereof. Further, one having a part thereof substituted with, diethylene glycol, 1,4-tetramethylene glycol, 1,4-cyclohexane dimethanol or heptanemethylene glycol in a case of a glycol component, or e.g. isophthalic acid, 1,5-naphthalene dicarboxylic acid or adipic acid in a case of a dicarboxylic acid component, as a copolymerizable monomer, may be used. Preferred is a polyethylene terephthalate type resin having from 0.1 to 10 mol % of a 1,4-cyclohexane dimethanol component as a glycol component copolymerized, or a polyethylene terephthalate type resin having from 1 to 10 mol % of an isophthalic acid component as an acidic component copolymerized, from the viewpoint of moldability.
More preferred is a polyethylene terephthalate type resin comprising a glycol component and from 1 to 10 mol % of a 1,4-cyclohexane dimethanol component copolymerized, since crystallization proceeds slowly, and the impact strength is high. With a copolymer with a higher molar ratio of the 1,4-cyclohexane dimethanol component, the crystallization proceeds extremely slowly, whereby there will be problems such as fusion and blocking in extrusion step, drying step or recycle step, or physical properties of a molded product tend to be deteriorated.
Further, one having an intrinsic viscosity [xcex7] (hereinafter referred to as IV value) of from 0.6 to 1.0 dl/g is suitably used, as measured at 30xc2x0 C. when the polyethylene terephthalate type resin is dissolved in a mixed solvent of 1,1,4,4-tetrachloroethane with phenol (in a weight ratio of 60:40). If it is less than 0.6, the electroconductive sheet or the molded product tends to have insufficient mechanical strength and is likely to break, and if it exceeds 1.0 dl/g, the melt viscosity tends to be high, and extrudability tends to be poor, whereby the productivity will decrease. As the polyethylene terephthalate type resin, a commercially available product may be used.
For the substrate layer, an imidated copolymer having an aromatic vinyl monomer residue and an unsaturated dicarboxylic acid imide derivative residue may be used. In such a case, it is preferred that the substrate layer further contains an acrylonitrile-butadiene-styrene copolymer type resin in addition to the imidated copolymer.
The imidated copolymer is a copolymer having an aromatic vinyl monomer residue and an unsaturated dicarboxylic acid imide derivative residue, and one further having an unsaturated dicarboxylic anhydride residue may also be used. It may further contain a rubber-like polymer. With respect to the amount of each component, the rubber-like polymer is from 0 to 40 wt %, the aromatic vinyl monomer residue is from 30 to 70 wt %, the unsaturated dicarboxylic acid imide derivative residue is from 20 to 60 wt %, and the unsaturated dicarboxylic anhydride residue is from 0 to 15 wt %. Further, a copolymerizable vinyl residue may be used in an amount of from 0 to 40 wt %. As the imidated copolymer, a commercially available product may be used, such as xe2x80x9cMaleccaxe2x80x9d trade name, sold by Denki Kagaku Kogyo K.K.
The acrylonitrile-butadiene-styrene copolymer type resin to be used in such a case is not particularly limited, and a commercially available product may be used. Particularly preferred is an acrylonitrile-butadiene-styrene copolymer type resin comprising from 5 to 93 wt % of a graft copolymer obtained by copolymerizing from 5 to 80 parts by weight of a rubber-like polymer with from 20 to 95 parts by weight of a monomer mixture comprising from 60 to 90 wt % of an aromatic vinyl monomer, from 10 to 40 wt % of a vinyl cyanide monomer and from 0 to 40 wt % of a vinyl monomer copolymerizable with the above monomers, and a resin composition comprising from 0 to 80 wt % of a vinyl copolymer comprising from 60 to 90 wt % of an aromatic vinyl monomer residue, from 10 to 40 wt % of a vinyl cyanide monomer residue and from 0 to 40 wt % of a vinyl monomer residue copolymerizable these with.
In a case of using an acrylonitrile-butadiene-styrene copolymer type resin together, the imidated copolymer may be used in an amount of from 5 to 93 wt % based on the total amount of the imidated copolymer and the acrylonitrile-butadiene-styrene copolymer type resin. If it is beyond this range, heat deterioration is likely to result during processing, or no adequate impact strength tends to be obtained.
Carbon black may be incorporated into the substrate layer of any composition, in a small amount so as not to impair the fluidity. By incorporating carbon black, the mechanical strength will further improve, and at the same time, such a problem can be overcome that the thickness of the electroconductive sheet tends to be thin when the electroconductive sheet is formed into a packaging container, whereby e.g. the corner portion of the packaging container may be transparent.
Carbon black to be incorporated in the substrate layer is not particularly limited, so long as it can be uniformly dispersed in the substrate resin. The amount of carbon black incorporated in the electroconductive substrate layer, may be within a range of not impairing the fluidity as mentioned above, and it is preferably from 0.1 to 10 wt % based on the thermoplastic resin.
Into the substrate layer of any composition, another known thermoplastic resin component such as a polyethylene resin or a polypropylene resin, an olefin type resin such as a copolymer of ethylene or propylene (such as an ethylene-ethylacrylate resin, an ethylene-vinyl acetate copolymer resin or an ethylene-xcex1-olefin copolymer resin), or a polyester type resin such as a polyethylene terephthalate resin or a polybutylene terephthalate resin, may be incorporated as a modifier. Further, an additive such as a lubricant, a plasticizer or a processing aid may be incorporated as the case requires. Further, for the substrate layer, the edge or a missed roll of the electroconductive sheet to be generated during production of the electroconductive sheet, or a pulverized product of the molded product, may be recycled in an amount of from 5 to 50 wt %.
To prepare the electroconductive sheet of the present invention, firstly a part or whole of the starting materials for the electroconductive resin composition is kneaded and pelletized by means of a conventional method employing e.g. an extruder, and the obtained electroconductive resin composition is sheeted together with a thermoplastic resin composition to be an electroconductive substrate sheet by a conventional method employing e.g. an extruder.
With respect to kneading of the electroconductive resin composition, starting materials may be kneaded all at once or may be stepwisely kneaded in such a manner that, for example, carbon black and a half of the polycarbonate type resin are kneaded, and then the rest of the materials are added to the kneaded product, followed by kneading, and it is also possible to add the rest of the materials at the time of sheeting.
The electroconductive sheet can be prepared by a known method employing e.g. an extruder or a calendering machine. As a method for laminating the electroconductive resin composition on the substrate layer, the respective layers may be firstly formed into sheets or films by a separate extruder and then stepwisely laminated by e.g. a thermolaminating method, a dry laminating method or an extrusion laminating method. Otherwise, the electroconductive resin composition may be laminated on the preliminarily formed electroconductive substrate sheet, by e.g. extrusion coating. In order to prepare the electroconductive sheet at a lower cost, it is preferred to obtain a laminated electroconductive sheet all at once by e.g. a multilayer coextrusion method employing a feed block or a multimanifold die.
The method for bringing the surface roughness Ra to be from 0.6 to 4.0 xcexcm is not particularly limited, but a method of incorporating an inorganic filler such as talc, calcium carbonate, mica or isinglass into the resin, a method of incorporating natural rubber or synthetic rubber, or a method of embossing the surface by an embossing roll, may be mentioned. The method of embossing the surface by an embossing roll has such advantages that the dynamic properties and fabrication properties of the electroconductive sheet will not be impaired, it can be widely applied to e.g. a vinyl chloride resin, a polycarbonate resin, a polystyrene resin or a polyethylene terephthalate resin, which is used as an electroconductive sheet for a carrier tape at the present time, and further, as a cover material, one which is conventionally used can be utilized as it is.
The entire thickness of the electroconductive sheet is preferably from 0.1 to 3.0 mm, and the thickness of the electroconductive resin composition layer is preferably from 2 to 80% of the entire thickness. If the entire thickness is less than 0.1 mm, the strength of the packaging container to be obtained by forming the electroconductive sheet tends to be inadequate, and if it exceeds 3.0 mm, forming such as pressure forming, vacuum forming or thermo-forming tends to be difficult. Further, if the thickness of the electroconductive resin composition layer is less than 2%, the surface resistivity of the packaging container obtained by forming such an electroconductive sheet tends to be so high that no adequate antistatic effects can be obtained, and it exceeds 80%, the processability in e.g. pressure-forming, vacuum-forming or thermoforming tends to be poor.
The electroconductive sheet of the present invention is useful as a packaging material for electronic parts such as IC or electronic parts using IC, and is used for injection-molded trays, vacuum-formed trays, magazines and carrier tapes, and it is particularly suitable for carrier tapes.
Now, the present invention will be explained in further detail with reference to Examples. However, it should be understood that the present invention is by no means restricted to such specific Examples.